I am developing a Flutter app and submitting it to App Store Connect and instantly get an email that the App was rejected because of
ITMS-90683: Missing Purpose String in Info.plist Your app's code references one or more APIs that access sensitive user data. The app's Info.plist file should contain a NSContactsUsageDescription key with a user-facing purpose string explaining clearly and completely why your app needs the data. Starting Spring 2019, all apps submitted to the App Store that access user data are required to include a purpose string. If you're using external libraries or SDKs, they may reference APIs that require a purpose string. While your app might not use these APIs, a purpose string is still required. You can contact the developer of the library or SDK and request they release a version of their code that doesn't contain the APIs. Learn more (https://developer.apple.com/documentation/uikit/core_app/protecting_the_user_s_privacy).
Supposedly there are 5 purpose strings missing.
It's right that my App is using the APIs listed in the email but I have the keys in my Info.plist file and when running the app on my iPhone the purpose strings are shown when the app requests the corresponging permissions from the user. I even translated the strings using InfoPlist.strings files in the folders en.lproj etc. In the Info.plist I referenced the translated string like this
<key>NSContactsUsageDescription</key>
<string>$(NSContactsUsageDescription)</string>
I already tried unpacking the .xcarchive (in Mac Finder right click -> Show Package Contents) and the .ipa files. In those I found the Runner.app (I think Runner is a Flutter specific "name") and also showed package contents. I found the Info.plist and when I open it in a TextEditor or also XCode the Strings are gone but the InfoPlist.strings files are still there.
I think that something goes wrong when exporting so that the values are cleared?